Showing papers by "Tao Tao published in 2012"

Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes

Abstract: The azo-hydrazone tautomerism of two pyridine-2,6-dione based Disperse Yellow dyes has been achieved by pH control and metal-ion complexation, respectively, which is evidenced by UV-visible spectra using pH-titration, 1H NMR and X-ray single-crystal diffraction techniques for two dyes and one neutral dinuclear dye–metal complex. pH-titration experiments under strong and weak acidic conditions (HCl and HOAc) as well as strong and weak alkaline conditions (NaOH and ammonia) demonstrate that there is an equilibrium between the azo (HL1-A and HL2-A) and hydrazone (HL1-H and HL2-H) tautomers for two dyes in solution but the hydrazone form is dominant under conventional conditions. The hydrazone proton is also observed in the 1H NMR spectra of HL1-H and HL2-H which can be verified by the hydrogen–deuterium exchange and the presence of cooperative six-membered intramolecular hydrogen rings involving the hydrazone proton in their X-ray single-crystal structures. Moreover, the azo-hydrazone tautomerism is evidenced by the formation of a novel neutral dinuclear dye–metal complex Cu2(L2-A)4, where all the ligands are in the azo form and two types of coordination modes are present for four L2-A ligands. Namely, the side two ligands serve as the bidentate capping ligands, while the middle ones act as the quadridentate bridging ligands linking adjacent CuII centers in a reverse fashion.

The First Observation of One-Dimensional Naphthalenediimidato-Based Transition-Metal Coordination Polymers: Syntheses, Crystal Structures and Properties

Abstract: Metal-directed assembly of naphthalene-1,4,5,8-tetracarboxylic acid (NTA) with different transition-metal salts in the presence of ammonia results in a series of one-dimensional metal−naphthalenediimidato (M−NDI) coordination polymers with the formulas of {(Ag(NDI))(NH4)}n (P1), (Zn(NDI)(NH3)2)n (P2), (Cd(NDI)(NH3)2)n (P3), (Co(NDI)(NH3)2)n (P4) and (Ni(NDI)(NH3)2)n (P5), respectively It is worthwhile to mention that the 1D straight-line NDI−Ag(I) coordination polymer P1 is formed stepwise from a dinuclear NDI−Ag(I) intermediate (Ag2(NDI)(NH3)2 )( 2AgNDI), where ammonia serves as a stabilizing reagent of Ag(I) ion and a weak base to remove the protons of NDIH2 simultaneously Furthermore, P1 exhibits semiconducting properties in the solid state which may originate from its all-parallel-aligned packing structure (AAAA) which is different from the common ABAB packing mode for P2−P5 and 2AgNDI In addition, theoretic computational studies as well as X-ray photoelectron spectrometer spectra on P1 and 2AgNDI have also been carried out

Comparative structural and spectral analyses for mononuclear and dinuclear metal complexes of 2-thiophen and 2-(5-bromothiophen) imidazo[4,5-f][1,10]phenanthroline

Abstract: A series of mononuclear and dinuclear mercury(I), mercury(II), nickel(II), lanthanum(III), ferrous(II) and ruthenium(II) complexes 4–11 with different metal/ligand molar ratios (1 : 1, 1 : 2 and 1 : 3), having 2-thiophenimidazo[4,5-f[[1,10[phenanthroline (TIP) and 2-(5-bromothiophen)imidazo[4,5-f][1,10[phenanthroline (5-Br-TIP) ligands, have been synthesized and structurally compared. In addition, three protonated salts of TIP and 5-Br-TIP (1–3) with PF6− and ClO4− counterions have been described herein where the proton is found to be located at one of the nitrogen atoms of 1,10-phenanthroline moiety. It is notable that the whole molecules of dinuclear mercury(I) and nickel(II) complexes 6 and 7 exhibit excellent planarity in the lengths of 2.52 and 2.90 nm, respectively. UV-Vis, 1H NMR and luminescence spectra of ligands TIP and 5-Br-TIP, protonated salts 1–3 and metal complexes 4–11 have also been studied and compared.

Raman Scattering Study of In x Ga 1 −x N Alloys with Low Indium Compositions

Abstract: InxGa1−xN alloys with low indium composition x in the range 0.13 ≤ x ≤ 0.23 are systematically studied mainly based on a Raman scattering technique. Scanning electron microscopy and x-ray diffraction results show that our samples can be divided into two groups: pseudomorphic (0.13 ≤ x ≤ 0.16) and relaxed (0.18 ≤ x ≤ 0.23). The prominent enhancement of A1 longitudinal-optical (LO) mode is found with 325 nm laser excitation. For pseudomorphic samples, the frequencies of A1 (LO) phonons agree well with the theoretical predictions, which verifies that the samples are fully strained. For relaxed InxGa1−xN samples, a linear dependence of the A1 (LO) mode frequency is obtained: Ω0(x) = (740.8 ± 3.3) − (143.1 ± 16.0)x, which is the evidence of one-mode behavior in InxGa1−xN ternary alloys. Residual strains in these partially relaxed samples are also evaluated.